The state of the California current, 1997-1998: Transition to El Nino conditions

This report, part of a continuing series of annual reports describing ocean ographic conditions in the coastal waters of the Californias, emphasizes th e 1997-98 period, The coastal waters of the Californias were strongly influ enced by El Nino conditions beginning late in the summer of 1997 and contin uing into the summer of 1998, Timely prediction of the onset of this event made it possible for several research programs to augment their observation programs. We review the pattern of atmospheric forcing and changes in the tropical ocean and note the initial impacts upon the California Current sys tem, Sampling being done by the CalCOFI (California Cooperative Oceanic Fis heries Investigations) program is described, and recent data are summarized and interpreted, Data from several other programs including oceanographic sampling off Baja California and central California, and coastal data from buoys, shore stations, and diving programs in kelp forests are reported, Th ere were large and rapid changes in atmospheric forcing and in the upper oc ean temperature and salinity distribution and circulation pattern. The pela gic ecosystem was strongly influenced; cruise mean macrozooplankton abundan ce during the spring of 1998 was the lowest in the 50-year CalCOFI time ser ies. Large changes in the range and abundance of plankton and fish populati ons were observed. El Nino-induced changes must also be considered in the c ontext of changes on other space-time scales, and the relation of El Nino-r elated changes and secular trends seen since the mid-1970s regime shift wil l merit particular attention.